The first key factor in creating the domestic slave trade was an insatiable
demand for labor from expanding plantation regions in the South. The second
essential element was the availability of a ready supply of enslaved people - a
supply made possible because North American slave numbers, unlike those
in the rest of the Americas, grew by natural increase (that is, numbers
of births exceeded numbers of deaths). By the 1730s, the enslaved populations
of Maryland, Delaware, and Virginia were rapidly growing. A decade or
so later, even those of colonies south of Virginia began to experience
continuous and rapid natural increase. In the latter colonies, though,
the expansion of the plantation regime was so great that the importation
of enslaved men, women, and children was seen as essential.

In the 1760s, Pennsylvania, New York, New Jersey, and Massachusetts were
exporting some of their bondspeople to the Southern colonies. This trend
is verified for example by evidence in the South Carolina
Gazette, where advertisements referred to numerous men and women who had been
brought from these Northern colonies. In the 1770s, slave traders, also
called
speculators, regularly advertised in the Boston
Gazette
for "healthy slaves, . . . Male or Female who have been some years
in the Country, of twenty Years of Age or under." As slavery declined
in the mid-Atlantic and northern states, owners began to sell their slaves
to traders who moved them further south. The scale of the trade from
the North is suggested by alarm in South Carolina that northern blacks
might undermine the discipline of the local enslaved population. In 1792, for example,
citizens of Beaufort, South Carolina, petitioned the state legislature
complaining about the "notorious" practice of Northerners, who
"have for a number of years past been in the habit of shipping to
these Southern states, slaves who are scandalously infamous and incorrigible."

The export trade from Delaware, Maryland, and Virginia was very
well established by the 1780s. At the Constitutional Convention of 1787,
Charles C. Pinckney explained that Virginia "will gain by stopping
importation [from Africa]. Her slaves will rise in value and she has more than she wants." South Carolina and Georgia whites called out for
slaves - and newspaper advertisements of 1787 show that Virginia was ready
to supply them. The trader Austin Moses advertised in Richmond, Virginia,
for: "One hundred Negroes from 20 to 30 years old for which a good
price will be given. They are to be sent out of state, therefore we shall
not be particular respecting character of any of them - hearty and well
made is all that is necessary."

Moses was one of many who regularly sent enslaved Virginians to the expanding
plantation regions further south and west.

The interregional movement of the enslaved population was made up of
two elements. The substantial majority - from 60 to 70 percent (or 1.2
million people) - migrated by the long-distance domestic slave trade, while the rest were part of planter migrations. In the latter case, planters
looking for new opportunities moved all or most of their slaves together
to work new western land.

By the 1790s, Maryland, Delaware, and Virginia had become the main exporting
areas, the bulk of their "shipments" going to Georgia, Tennessee,
Kentucky, the Carolinas, and the sugar-planting regions of Louisiana.
But by the 1820s the Carolinas and Kentucky were exporting more people than they were importing.

Thirty years later, Tennessee, Missouri, Georgia and Alabama had joined
the ranks of net exporters. From 1760 until the Civil War, the number
of men, women, and children traded to the South and West increased substantially
during each decade, with the exception of the 1840s when numbers slackened.

Some historians have argued that selling south occurred because land
in the exporting states was exhausted. According to this argument, "soil
exhaustion" meant that agriculture was in decline in the exporting
states, and those states could not support a growing slave population.
This traditional argument seems to misrepresent the true situation, however.
In fact, farming still flourished in the exporting states, but selling people
offered the chance of further profit. For example, in South Carolina during
the 1850s, 65,000 African Americans were transported out of state, but
still the states cotton production rose by 50,000 bales and its enslaved
population increased by seventeen thousand.

The trade was motivated purely by profit, and enslaved men, women, and children went to markets
that offered the highest profits. Some were sold at major
urban marketplaces such as New Orleans and Natchez, but most were dispatched
directly to scattered rural communities.

In 1846, speculator T. W. Burton wrote from Lowndes County, Alabama,
"There is a vast quantity of negroes in the Market here" and
traders were offering slaves in every village in the county. The area,
he said, was "full of negroes." Moving on to Mississippi, Burton
found that "there is negroes [offered by traders] all through the
state." Most traders covered several counties in seeking out buyers.
A fellow speculator reported that Dr. Thomas C. Weatherly, a typical trader,
"Lives in his tents. He told me he sold ten negroes last week at
fair prices. [As a means of meeting customers] he is following the counties
round attending the courts."